Phylogenetic and chemotaxonomic significance of diterpenes in some Portulaca species (Portulacaceae)

An instance is presented in which skeletal features of chemical constituents provide valuable information on the phylogenetic relationship in plant species. A close examination of diterpenoid constituents was carried out on three Portulaca species, each of which has a different basic chromosome number. Major diterpenoid constituents in P. cv. Jewel, P. pilosa and P. grandiflora were found to be, respectively, of the clerodane ([6.6]-fused ring), prinziane ([7.6]-fused ring) and portulane ([7.5]-fused ring) types. From a biosynthetic viewpoint, a linear evolutionary relationship among the Portulaca plants in question would be assumed. All the diterpenoids found in the above three species have 1,4-dihydroxy-2-buten-2-ylethyl side chains and the relevance of this feature for chemical systematics of Portulaca plants is pointed out.